1. Field of the Invention
This invention relates to a brake power servo booster. More particularly, it is concerned with a brake power servo booster in which a movable stop provided on an input shaft is caused to abut on a stationary stop provided in the cylindrical projection of a rear shell to restrict the retracted position of the input shaft.
2. Description of the Prior Art
There is known a brake power servo booster having a stationary stop and a movable stop which restrict the retracted position of an input shaft to reduce or eliminate the ineffective stroke of the input shaft during the initial period of booster operation. The input shaft is connected to a brake pedal by a coupling which is usually called a clevis. In order to minimize the space for the installation of the booster in an engine room, it is desirable to shorten the input shaft and allow the coupling to move into the cylindrical projection of a rear shell as the input shaft advances during the operation of the booster. This requires a sufficiently large space in the cylindrical projection to admit the coupling which is considerably large. The stationary stop, which is provided in the cylindrical projection, has to be disposed radially outwardly of the space for the coupling. It is necessary to enlarge accordingly the diameter of the movable stop which is provided on the input shaft.
The input shaft is swingable in accordance with the arcuate motion of the brake pedal. The angle of the input shaft in its swung position to the axis of the cylindrical projection depends slightly on any error in the positioning of the booster on the vehicle body, the position at which the input shaft is coupled to the brake pedal, or any change in that position resulting from the adjustment of play on the brake pedal. This variation in the angle has an effect on the relative positions of the stationary and movable stops, especially when the movable stop has an enlarged diameter. An increase in the diameter of the movable stop brings about a greater displacement of its outer periphery along the axis of the input shaft when it is swung. This displacement has an adverse effect on the position to which the movement of the input shaft is restricted by the abutment of the movable stop on the stationary stop.